Lentigo Maligna
Hutchinson's melanotic freckle, premalignant melanosis of Dubreuilh.
This lesion is on the leg of an elderly gentleman. Given its irregular borders, pigmentation and history of recent growth, this lesion may be either lentigo maligna or lentigo maligna melanoma.
This lesion is two tone, has irregular borders and is on an area of sun exposure. Adequate removal of this lesion presents a reconstructive challenge.
Features
Lentigo maligna (LM) is characterised by lentiginous replacement of basal keratinocytes by atypical melanocytes with no downward invasion into the underlying dermis. This is malignant melanoma in situ which can progress to a superficial or nodular melanoma. Every effort should be made to identify and treat this lesion before invasion of the underlying dermis occurs. That said, it appears that the estimated risk of LM progressing to LM melanoma is 5% in those diagnosed with LM at 45 years of age.
Clinically, lentigo maligna appears as a flat, often two-tone, brown lesion with irregular borders. It tends not to be associated with pre-existing skin lesions such as naevi. It is most often found in the elderly on chronically sun exposed areas such as the face.
Incidence
Lentigo maligna is melanoma in situ. This can progress to lentigo maligna melanoma.
Aetiology
See malignant melanoma
Differential Diagnosis
Benign lentigo. Actinic keratosis.
Treatment
Excision biopsy is the ideal. Unfortunately, due to the often facial site of the lesion, sometimes excision biopsy is not possible due to the local tissue destruction which this would entail. In these circumstances, incisional biopsy of the darkest areas of the lesion would be appropriate.
After lentigo maligna has been confirmed, standard excision of the lesion with 5 mm margins is sufficient in 50% of cases. The recurrence rate with standard excision ranges from 8 to 20%. The recurrence rate has been found to be as low as 4-5% with Moh's surgery.
Topical 5-fluorouracil and cryotherapy have also been shown to be of use, however the risk of recurrence is high and neither treatment reduces the likelihood of developing invasive disease.
Several small scale studies also report the use of radiotherapy in lentigo maligna with good recurrence free intervals and excellent cosmetic result.
